Method of water well maintenance-time based approach

Abstract

A method of preventive well maintenance with pumping equipment in the well for well rehabilitation using CO2 with varying lengths of producing intervals utilizing varying methods to deliver cleaning energy and varying porosity of aquifers to determine varying quantities of energy over the entire well structure.

Description

Field of the Invention

[0001] The present invention relates to an improvement in a method of preventive well maintenance with pumping equipment in the well.Background of the Invention

[0002] Aqua Gard ®< is an innovative well cleaning process that moves away from the traditional approach in the groundwater well industry of operating a well until failure. The goal of moving away from the operation until failure mentality is to target materials that build up in the near well environment (which is a natural occurrence in almost all wells) when they are soft and easy to remove. Most of the deposited material is soft until complete mineralization takes place over time. By scheduling cleaning events on a time interval approach, materials that would eventually become difficult to move are easily removed from the well, and surrounding filter pack and near aquifer.

[0003] With the installation of permanent Aqua Gard ®< equipment in a well, cleaning events can take place without the need to remove the pumping or injection equipment. Removal and replacement of pumping equipment during cleaning events adds a lot of downtime and cost to typical well cleaning events. The mentality of minimizing the downtime while maintaining quantity and quality of water pumped from a well is paramount to the model of protecting a well that Aqua Gard ®< typifies.

[0004] Aqua Gard ®< is a well cleaning process that utilizes natural carbon dioxide (CO 2 ), allowing easier compliance with regulatory discharge as well as better distribution of cleaning energy throughout the well, filter pack and the surrounding aquifer. Cleaning a well requires energy. Combination energies may be required to get the entire well structure cleaned effectively. Most of the energy utilized in the Aqua Gard ®< process is provided by the various phases of carbon dioxide (CO 2 ). The phase in which CO 2 occurs is a function of temperature and pressure, and in well environments, all three major phases of CO 2 (solid, liquid, and vapor) can occur. Aqua Gard ®< involves the controlled injection of liquid and vapor phases of carbon dioxide. As liquid CO 2 is injected into the well, the pressure and temperature encountered at the injection point do not initially provide a stable environment for liquid CO 2 to exist. The CO 2 therefore undergoes a phase change to vapor. The phase change of CO 2 from a liquid to a vapor can cause a volume expansion of up to 570 times. This volume expansion is one of the sources of energy that provides the cleaning action and agitation inside the well and the near well environment.

[0005] Another source of energy is the thermodynamic cooling of the water in the well due to the controlled injection of liquid CO 2 (liquid and solid CO 2 can be very cold). When the water gets cool enough, it can freeze. Solid water (ice) has a larger volume than liquid water, and the formation of ice can break up and loosen materials that are clogging pore volume in a well.

[0006] There are many different aspects to the energy delivered into a well with the Aqua Gard ®< process that can be utilized. Deliver energy into the well in the form of CO 2 liquid, and vapor resulting in phase changes of liquid to vapor, liquid to solid, and solid to vapor (sublimation) occurs. This has been demonstrated to be the most effective way to deliver energy that loosens clogging materials. The Aqua Gard ®< process is economical and restores the pumping capacity of a well, and eliminates the need to neutralize and dispose of chemicals that can be dangerous.

[0007] EP 1 339 937 A2 and WO 01 / 98628 A1 describe the use of multiple pipes within a well for purpose of injecting energy and to activate the injection lines by injecting in various sequences to mobilize sediments from the bottom of the well.

[0008] DE 100 23 454 A1 describes the use of carbon dioxide to clean a well having a filter tube with vertical gravel bed. Pneumatic pressure waves are introduced into the area of the filter tube and into the gravel bed from outside, at set or selected time intervals, wherein the pressure waves are generated by the use of carbon dioxide. The appliance has a pressure vessel connected via a controlled valve to a feed tube, which is placed in the ground outside the filter tube, wherein the tube is connected to pneumatic discharge nozzles for the pressure waves located in a ring around the filter tube and the valve is connected to a timer.Summary of the Invention

[0009] It is an object of the present invention to improve the Aqua Gard ®< process by providing a better distribution of effective energy into all parts of a producing interval of a well that has a long producing interval.

[0010] It is also an object of this invention to provide a challenge for distributing energy over the entire well structure. The distribution of energy into all parts of the well includes the upper casing, the producing interval of a well screen or open hole rock well, the filter pack and into the surrounding formation.

[0011] The present invention relates to a method of preventive well maintenance with pumping equipment in the well using CO 2 , wherein the well is sealed, wherein a distribution of energies comprising the combination of mechanical energy, chemical energy and thermal energy is provided throughout an entire well structure including all parts of the producing interval of the well and surrounding formation and distributing said energies throughout the entire well structure by controlling CO 2 phase changes during CO 2 injection to cause surging agitation within the well bore and surrounding formation and allowing said energies to reach substantially all areas of the well, wherein the method further comprises setting a volume displacement pipe into the well prior to carbon dioxide injection, wherein the volume displacement pipe has a smaller diameter than a well screen or borehole wall to displace water in the well and to direct the energies more effectively to the well screen or fractures of a rock well, characterized in that an injection nozzle for carbon dioxide is directed at a desired angle to achieve a vortex in an annular space between the Volume Displacement Pipe (VDP) and the well screen or borehole wall, and wherein the vortex distributes said energies more efficiently throughout the well and surrounding aquifer.

[0012] Preferably, a volume of carbon dioxide energy resulting in less penetration of solubilized carbon dioxide into surrounding formations is selected, resulting in less pump development time prior to returning the well back to ambient or pretreatment conditions, wherein in addition to a porosity of an aquifer, selecting the volume of said energies by evaluating a buffering capacity of the aquifer, wherein the buffering capacity can be determined by assessment of an amount of carbonates in the aquifer and a total alkalinity of the water.

[0013] Moreover, carbon dioxide is injected into a sealed well to surge the well by switching between liquid CO 2 injection and vapor CO 2 injection cycles, wherein the length of cycles is calculated based upon a length of a producing interval and a flow rate of carbon dioxide.

[0014] The distribution of energy can be achieved with combination energies including environmentally friendly chemicals that can be carried and distributed with the use of carbon dioxide energy in a sealed well. Carbon dioxide phase changes create agitation of the chemistries, allowing them to reach all areas of the well. Combination energies are necessary when wells have long producing intervals.

[0015] Improvements to the existing Aqua Gard ®< approach involve using combination energies to achieve more equal distribution of energies. The combination of chemical energy, thermal energy and mechanical energy are produced by the phase changes of liquid to vapor, liquid to solid and solid to vapor of carbon dioxide.

[0016] Chemical energy provided by National Science Foundation (NSF) approved proprietary chemicals are effective on mineral solubility, and effective on biological dispersion and disinfection, metal dispersion and clay dispersion. Placing chemistry in the well and utilizing the agitation of the carbon dioxide phase changes delivers the chemical energy to all portions of the well.

[0017] Quick release pulsing energy devices can be placed in the bottom of the well. These devices can store energy which can be released at high pressure, allowing disruptive energy to be released that can mobilize fines in the surrounding filter pack and formation. Once the energy is released, pressure rebuilds for another rapid release, and the cycle repeats until such time as energy is no longer introduced into the quick release device. If a pressure relief valve is selected as the energy delivery mechanism, it is selected based upon hydrostatic pressure. The pressure relief valve would utilize liquid and vapor phases of carbon dioxide, and would be designed to close after release to allow pressures to build up again.

[0018] Biological fouling and associated minerals on the surfaces within the water well environment can be measured with the use of low voltage resistive devices that can be permanently placed in the well. This would allow the cleaning cycle to be initiated when the surfaces are fouled or have evidence of deposited material.

[0019] A coating on a sensor in the low voltage resistive device would identify a change in the electrical voltage in the wires that are hooked up to the resistor. In many wells where low voltage resistive devices will not be able to be installed for various reasons, it is important to maintain the time interval approach. Presently, without resistive devices, there is no good indicator of when a well should be cleaned.

[0020] The method of calculating the specific capacity of a well is an industry standard and is still in use today as an indicator of the productive capacity of a well. Specific capacity is defined as the volume of water removed from a well per unit of drawdown (GPM / FT). As the well is operated over time, and the natural well clogging processes proceed, the specific capacity of a well will go down.Brief Description of the Drawing

[0021] Fig. 1shows a screened well with a filter pack with pump in the well. Fig. 2is a figure representing the different flow regimes. Detailed Description of the Invention

[0022] Fig. 1 represents the advantage of a variable interval injection cycle. When the well is being injected with liquid CO 2 , the water becomes supersaturated with carbon dioxide. When a transition is made at the injecting valve from liquid to vapor CO 2 , the water that was filled with CO 2 releases the CO 2 and the water level quickly drops. Switching from liquid back to vapor results in a very sudden surge as water flows rapidly back into the well. This sudden surge back into the well can further disrupt attached material and mobilize detached clogging material as well as bringing fines from the surrounding aquifer that have invaded the pore spaces surrounding the well.

[0023] Manipulating the injection intervals of vapor and liquid improves the efficiency and the effectiveness of the cleaning process, and the surge created by the change between liquid and vapor is maximized by lengthening the liquid time intervals and shortening the vapor injection intervals.

[0024] The surging effect is caused in the well by the change in concentration of the bubbles in the well. When liquid CO 2 is injected into the well, the concentration of bubbles in the well is very high, and the surface of the water in the well is very agitated. The high concentration of bubbles in the well results in the movement of a high concentration of vapor upwards in the well, creating a buoyancy effect. When a transition is made in the controlled injection of CO 2 from the liquid phase to the vapor phase, the high concentration of bubbles becomes much lower and the water level in the well falls quickly.

[0025] Essentially, the volume in the water column that was filled with the high concentration of vapor collapses as the high concentration of CO 2 (liquid injection) ceases. In addition to the buoyancy effect during the liquid CO 2 injection, the water level in the well is forced downward with gases coming out of solution, and switching back to vapor results in water rushing back into the well, creating a surging effect. Maximizing the surging caused by the transition from liquid to vapor can be done by calculating the volume of liquid required to create the 'buoyancy' effect.

[0026] When the desired buoyancy effect is reached, a switch to the vapor injection can be made. With an understanding of the delivery pressure and flow of the CO 2 into the well, a timing mechanism can be used to deliver the liquid and vapor phases of CO 2 . The control of the delivery with a timing mechanism will maximize this surging effect, ensuring that the delivery of the different phases creates the highest amount of water movement in the well.

[0027] In addition to maximizing the surging effect that the transition from liquid CO 2 to vapor CO 2 has on the water column, a greater control of the delivery of CO 2 to the well can maximize another form of energy delivery in the well during injection. Multiphase flow demonstrates that there are two forms of multiphase flow that the Aqua Gard ®< process entails.

[0028] The first form of multiphase flow is the direct delivery of CO 2 into the well. The CO 2 will travel in the delivery equipment in three different forms, vapor only, liquid only, or vapor and liquid blend, depending on how the operator controls the injection. There are a multitude of flow regimes in which a two-phase fluid will flow in a vertical water column, bubbly, slug, churn, annular, and wispy-annular. The flow regime that the fluid will flow in is based on the concentration of vapor versus liquid, as well as the velocity of the liquid in the pipe. A determination of the best way to deliver the CO 2 mixture will be made, and flow through the delivery pipe can be controlled with a flow control device to deliver the CO 2 in the method determined. The determination for the best way to deliver the CO 2 will be made based on which fluid flow regime provides the most effective way of creating 1) the surging effect caused by the transition of liquid to vapor in the injection process and 2) the vortex effect. The flow regime of CO 2 delivery would be targeted by the effect the chosen regime has on the Aqua Gard ®< process.

[0029] The second aspect is the multi-phase flow beyond the injection point. As the liquid and vapor phases enter the well, and the liquid phase changes to vapor, a new multi-phase regime is encountered where the liquid phase is the water in the well and the vapor phase is the rising CO 2 vapor. The goal of this second flow regime is to remove the most amount of clogging material. An inspection of Fig. 2 shows that certain flow regimes look more disruptive than other flow regimes. Particularly, the bubbly and annular regimes do not seem to be as disruptive as the slug or churn regimes. The injection would be controlled according to the multi-phase regime, which would disrupt the near well environment the most.

[0030] Fig. 1 shows a screened well with filter pack with pumping equipment in the well.

[0031] The different types of water wells can include, e.g., water supply wells, injection wells, aquifer storage and recovery (ASR) wells, recovery wells, monitor wells, collector wells, slant wells, horizontal wells, directional wells, etc.

[0032] Fig. 1 represents a very common type of water well, but many different types of wells require time based cleaning as determined by the application of the "Mansuy Principle".

[0033] The "Mansuy Principle" was established with the recognition that loss of specific capacity (discharge rate / drawdown) of a pumping well does not occur until significant clogging of pore space of the well screen 10, the filter pack 11 and the surrounding formation has become significant, and the remaining pore space of a well begins to transition from laminar to turbulent flow. Loss of specific capacity in any well will occur at a precise moment.

[0034] The "Mansuy Principle" of time based cleaning is based on not detecting that exact moment of pore space plugging. The "Mansuy Principle" establishes time based cleaning of a well when deposited plugging material is often soft and easy to remove. The cleaning sequence is performed with the pumping or injection equipment in the well 2, and utilizing the pump to pump the detached deposits, thus minimizing equipment needed to clean a well 2. Wells 2 have excess pore space when placed in production, and that exact moment of loss of specific capacity is after extensive plugging deposits have become established and the plugging deposits become mineralized and hardened, making their removal more difficult. Much of that excess pore space can be clogged but does not result in loss of specific capacity because extra pore space exists within the depth in a well and extra pore space exists further into the surrounding formation.

[0035] Any other type of well, including open hole rock wells, would be cleaned with the claimed invention. Water wells 2 are sealed with flange or a packer placed inside well casing 14. Carbon dioxide or selected chemicals are introduced into the water well 2 through injection line 1, 3 with pumping equipment in the well.

[0036] The chemicals, if used, must be approved to be placed into a water well 2. Carbon dioxide in various intervals is introduced into the well through injection line 1, 3, and regulated based upon injecting energy into a sealed well 2 at safe pressures, and monitored by pressure gauge 5 through a port 15. The non-pumping water level or static water level 8 is represented by 8 in Fig. 1. Injecting carbon dioxide into a sealed well 2 does require a well 2 to have some grout 6 around the well casing 14.

[0037] The intervals of carbon dioxide in both gaseous and liquid phase are introduced based upon the art of cleaning process to achieve maximum energy distribution. With very long screens or open hole intervals, chemical energy and carbon dioxide energy can be distributed over the entire well 2 and penetrate the combination energies into the filter pack 11 and the surrounding formation. The energy release from phase changes of carbon dioxide is necessary to distribute energy over the entire well structure 2 and into the surrounding formation in the zone of a water well that is plugged with mineral, biological and fine material from the aquifer 13.

[0038] A reduced amount of carbon dioxide and / or chemical energy is utilized with the volume displacement pipe 7 or suction flow control device. The volume displacement pipe 7 or suction flow control device also directs the carbon dioxide or combination energies to where plugging deposits occur. Carbon dioxide injected into a sealed well 2 through injection pipe 1, 3 through diversion elbow 4 creates a vortex 12 in the reduced annular space 9. The vortex 12 allows the combination energies to be distributed from the injection point represented by diversion elbow 4 and upward inside the well 2, allowing the entire well 2 and near well 2 to be cleaned more effectively.

[0039] The volume displacement pipe 7 or suction flow control device can reduce the amount of energy needed to clean the entire well 2, with less energy penetrating into the surrounding formation. With less energy penetrating into the surrounding formation, less time is required to return the well 2 to ambient or pretreatment conditions. Following the injection of energy into the sealed well 2 with a pump in the well 2, the gases from carbon dioxide are dissipated by allowing the energy inside the well 2 contact time, allowing effective cleaning of the well 2.

[0040] Usually the following day, the pump is operated and the well 2 flushed of all detached and solubilized plugging deposits. The flow sleeve or suction flow control device flushes the lower zones in the well by inducing flow through the extended pump suction. The volume displacement pipe 7 or suction flow control device, in addition to reducing the volume of energy required and directing the selected energy into the well and formation, also serves the purpose of a flow sleeve to cool submersible pump motor.

[0041] In addition to cooling the submersible pump motor, the extended flow sleeve more effectively serves the purpose of flushing the well 10, 11, 14 more effectively. More effective flushing with the use of the flow sleeve leaves the well in a cleaner condition, and flushes the planktonic bacteria more effectively.

[0042] Carbon dioxide induced vortex 12 creates a swirling action in the well 2 that can be maximized. The vortex 12 can be beneficial in the delivery of the energy provided by the carbon dioxide, and can utilize directional flow on the injection equipment to direct flow in the desired direction. The use of drop pipe or a suction flow control device (SFCD) to take up the space in the center of the well will focus the energy provided by the carbon dioxide phase change or combination energies towards the surfaces of the well 2 and surrounding filter pack 11 and aquifer 13. The vortex 12 will swirl upward in the annular space 9 between the SFCD and the well surfaces that are being cleaned. This vortex 12 can be utilized in the combination of carbon dioxide with chemical energy to further enhance the delivery of chemical energy. The smaller volume between the SFCD or pump suction and the well 2 / filter pack 11, well 2 / aquifer 13 interface would allow less carbon dioxide and / or chemicals to be utilized while achieving the desired cleaning effect. This will result in less impact on the surrounding aquifer 13, thus requiring less time to pump and flush the well in the impacted zone.

[0043] Fig. 1 shows a screened water well 2 with a filter pack 11. Any other type of well 2, including open hole rock wells, would be cleaned with the same steps. Water wells are sealed with flange or a packer placed inside well casing 14. Carbon dioxide or selected chemicals are introduced into the water well through injection line 1, 3.Improved energy distribution diagram elements list (Fig. 1):

[0044] 1: Energy Injection port 2: Well sealed with flange - Can also utilize a packer 3: injection line into lower part of the well 5: Pressure gauge to measure internal well pressure 6: Grout seal 7: Volume displacement pipe 8: Static water level 9: Reduced annular space between well casing and screen or open hole and volume displacement pipe or suction flow control pipe 10: Well screen or borehole face of rock well 11: Filter pack or natural pack 12: Vortex created by carbon dioxide injection and directional valve 13: Consolidated or unconsolidated aquifer 14: Well casing 15: Port through sealed well 18: Drop pipe or column pipe

Claims

1. A method of preventive well maintenance with pumping equipment in the well (2) using CO2, wherein the well is sealed, wherein a distribution of energies comprising the combination of mechanical energy, chemical energy and thermal energy is provided throughout an entire well (2) structure including all parts of the producing interval of the well (2) and surrounding formation and distributing said energies throughout the entire well (2) structure by controlling CO2 phase changes during CO2 injection to cause surging agitation within the well (2) bore and surrounding formation and allowing said energies to reach substantially all areas of the well, wherein the method further comprises setting a volume displacement pipe (7) into the well (2) prior to carbon dioxide injection, wherein the volume displacement pipe (7) has a smaller diameter than a well screen (10) or borehole wall (10) to displace water in the well and to direct the energies more effectively to the well screen (10) or fractures of a rock well, characterized in that an injection nozzle (3) for carbon dioxide is directed at a desired angle to achieve a vortex (12) in an annular space (9) between the Volume Displacement Pipe (VDP) (7) and the well screen (10) or borehole wall (10), and wherein the vortex (12) distributes said energies more efficiently throughout the well (2) and surrounding aquifer (13).

2. The method of claim 1, characterized in that phase changes of CO2 are utilized to distribute environmentally safe chemicals throughout the entire well (2) structure.

3. The method of claim 1, characterized in that a volume of carbon dioxide energy resulting in less penetration of solubilized carbon dioxide into surrounding formations is selected, resulting in less pump development time prior to returning the well (2) back to ambient or pretreatment conditions.

4. The method of claim 3, characterized in that, in addition to a porosity of an aquifer (13), selecting the volume of said energies by evaluating a buffering capacity of the aquifer (13), wherein the buffering capacity can be determined by assessment of an amount of carbonates in the aquifer (13) and a total alkalinity of the water.

5. The method of claim 1, characterized in that carbon dioxide is injected into the sealed well to surge the well by switching between liquid CO2 injection and vapor CO2 injection cycles, wherein the length of cycles is calculated based upon a length of a producing interval and a flow rate of carbon dioxide.

6. The method of claim 1 characterized in that a vapor CO2 injection cycle is shortened and more frequent cycles of liquid CO2 intervals are used, creating surging of a water column thus increasing the frequency of intervals between liquid and vapor CO2 and maximizing the surging effect.

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